Reconstruction of Extinct Shark Shows Early Evolution of Suction Feeding

Reconstruction of Tristychius arcuatus, an extinct type of shark that lived in the Carboniferous period. (Nobu Tamura via Wikipedia)

(CN) – A group of researchers have assembled a construction kit for a spiked-fin shark that may have lived 300 million years ago in order to understand how this fish got its jaws around its prey.

The Tristychius was approximately two feet long, resembled a modern-day dogfish and stalked near the waters of what is now Edinburg, Scotland.

Now, 335 million years after the sharks roamed, researchers from the University of Chicago say they understand the mechanics of their jaw, which resembled that of common bony fish such as bass, perch, carp and nurse sharks with their relatively small mouths.

Tristychius fossils, like many other shark fossils, are difficult to come by because cartilage skeleton usually rots away before the fossilization process can begin. When complete skeletons are found encased in rock, attempts to extract them whole tends to result in them falling to pieces.

University of Chicago professor Michael Coates and his team developed a CT imaging technology that can explore the fossils by creating a three-dimensional plastic printout of the cartilages to rebuild the shark’s skull.

Scans allow the team to avoid having to remove fossils from stone. Using modeling software, they can recreate the jaw movement of a Tristychius.

This small shark sucked water in through its mouth to catch prey from the ocean floor. That means these suction feeders could funnel water back out through their gills, a technique improved by their flexible arches and joints that expanded their cheeks and the volume inside their mouths, according to the study.

“Among today’s aquatic vertebrates, suction feeding is widespread, and is often cited as a key factor contributing to the spectacular evolutionary success of ray-finned fishes,” Coates said.

Researchers theorize that Tristychius jaws are some 50 million years older than similar jaws that adapted to suction feeding and further proof that sharks’ ability to feed evolved after one of the five big extinctions so they could better hunt.

Researchers found that the Tristychius tapped into virgin territory: While their cousin sharks were snapping their jaws at their prey, the suction feeders could eat from shallow burrows.

“These particular sharks were doing something sophisticated and new. Here we have the earliest evidence of this key innovation that’s been so important for multiple groups of fishes and has evolved repeatedly,” Coates said.